The present invention relates to a heater of the immersion type intended for use in an aquarium tank, and provided with a thermostat for setting and maintaining a desired temperature within the aquarium tank.
Heaters of the foregoing type equipped with thermostats are known. Typically, a thermostat or a thermoregulating device is provided on the heater to maintain the aquarium water within the temperature range compatible with the living conditions required for the fish.
Heaters may be of various types, including a heating element, e.g. heating coil enclosed in a glass container for immersion in the aquarium water. A thermostat which can be provided on the same container can be adjusted to various operating temperatures.
A thermostat or thermoregulator disclosed in EPC Publication No. 228,521 is formed by a bimetal strip which includes two contacts one of which is fixed and another is movable. When the temperature lowers the bimetal deforms and the contacts of the bimetal strip are closed. Current is then supplied to the heating element through the bimetal strip. This thermostat includes an externally rotated cylindrical element which is provided with a spiral line on its lateral surface. The line divides the cylindrical surface of the element into two differently colored portions which are visible through a longitudinal slot formed in a screen covering the cylindrical element and carrying a scale. The cylindrical element is axially coupled to a screw which bears down on one of the bimetal strips to bend it with respect to the other bimetal strip. Rotating of the cylindrical element by means of an external knob adjusts the relative spacing between the contacts. At the same time it positions the separation boundary between the two colored portions to a point on the scale corresponding to the desired temperature. The bimetal strips are calibrated to this temperature. The problem with this prior art thermoregulating device is that the line dividing two different colored portions may hardly be visible through the narrow slot and this makes the device difficult to adjust to a working temperature each time when desired. Another disadvantage of the known thermostat resides in that it comprises a large number of elements and is quite expensive to make.
Accordingly, there is need for a heater and thermostat unit of the immersible type which is easy to operate and less expensive to manufacture.